grokcore.component Grok-like configuration for basic components (adapters, utilities, subscribers) This package provides base classes of basic component types for the Zope Component Architecture, as well as means for configuring and registering them directly in Python (without ZCML). .. contents:: How to set up ``grokcore.component`` ==================================== In the following we assume you're writing or extending an application that does bootstrap configuration using ZCML. There's always a single ZCML file that is executed when the application is started, which then includes everything else. Let's assume this file is called ``site.zcml`` (that's what it's called in Zope), so that file is what we'll be editing. In order to register the components that you wrote using the base classes and directives available from ``grokcore.component``, we'll use the ``<grok:grok />`` ZCML directive. But before we can use it, we need to make sure it's available to the ZCML machinery. We do this by including the meta configuration from ``grokcore.component``:: <include package="grokcore.component" file="meta.zcml" /> Put this line somewhere to the top of ``site.zcml``, next to other meta configuration includes. Now, further down the line, we can tell the machinery in ``grokcore.component`` to register all components in your package (let's say it's called ``helloworld``):: <grok:grok package="helloworld" /> To sum up, your ``site.zcml`` file should look like something like this:: <configure xmlns="http://namespaces.zope.org/zope" xmlns:grok="http://namespaces.zope.org/grok"> <!-- do the meta configuration to make the ZCML directives available --> <include package="zope.foobar" file="meta.zcml" /> <include package="zope.frobnaz" file="meta.zcml" /> <include package="grokcore.component" file="meta.zcml" /> <!-- now load the configuration of packages that we depend on --> <include package="zope.barfoo" /> <include package="zope.somethingorother" /> <!-- finally load my components which are based on grokcore.component --> <grok:grok package="helloworld" /> </configure> Examples ======== Adapter ------- Here's a simple adapter that may be useful in Zope. It extracts the languages that a user prefers from the request:: import grokcore.component from zope.publisher.interfaces.browser import IBrowserRequest from zope.i18n.interfaces import IUserPreferredLanguages class CookieLanguage(grokcore.component.Adapter): """Extract the preferred language from a cookie""" grokcore.component.context(IBrowserRequest) grokcore.component.implements(IUserPreferredLanguages) # No need to implement __init__, it's already provided by the base class. def getPreferredLanguages(self): # This an adapter for the request, so self.context is the request. request = self.context # Extract the preferred language from a cookie: lang = request.cookies.get('language', 'en') # According to IUserPreferredLanguages, we must return a list. return [lang] Multi-adapter ------------- Here's a multi-adapter that functions as a content provider as known from the ``zope.contentprovider`` library. Content providers are components that return snippets of HTML. They're multi-adapters for the content object (model), the request and the view that they're supposed to be a part of:: import grokcore.component from zope.publisher.interfaces.browser import IBrowserRequest from zope.publisher.interfaces.browser import IBrowserPage from zope.contentprovider.interfaces import IContentProvider class HelloWorldProvider(grokcore.component.MultiAdapter): """Display Hello World!""" grokcore.component.adapts(Interface, IBrowserRequest, IBrowserPage) grokcore.component.implements(IContentProvider) def update(self): pass def render(self): return u'<p>Hello World!</p>' Global utility -------------- Here's a simple named utility, again from the Zope world. It's a translation domain. In other words, it contains translations of user messages and is invoked when the i18n machinery needs to translate something:: import grokcore.component from zope.i18n.interfaces import ITranslationDomain class HelloWorldTranslationDomain(grokcore.component.GlobalUtility): grokcore.component.implements(ITranslationDomain) grokcore.component.name('helloworld') domain = u'helloworld' def translate(self, msgid, mapping=None, context=None, target_language=None, default=None): if target_language is None: preferred = IUserPreferredLanguages(context) target_language = preferred.getPreferredLanguages()[0] translations = {'de': u'Hallo Welt', 'nl': u'Hallo Wereld'} return translations.get(target_language, u'Hello World') Of course, it's silly to implement your own translation domain utility if there are already implementations available in ``zope.i18n`` (one that reads translations from a GNU gettext message catalog and a simple implementation for tests). Let's try to reuse that implementation and register an instance:: import grokcore.component from zope.i18n.interfaces import ITranslationDomain from zope.i18n.simpletranslationdomain import SimpleTranslationDomain messages = {('de', u'Hello World'): u'Hallo Welt', ('nl', u'Hello World'): u'Hallo Wereld'} helloworld_domain = SimpleTranslationDomain(u'helloworld', messages) grokcore.component.global_utility(helloworld_domain, provides=ITranslationDomain, name='helloworld', direct=True) Global adapter -------------- Sometimes, you may have an object that should be registered as an adapter factory. It may have come from some other framework that configured that adapter for you, say, or you may have a class that you instantiate many times to get different variations on a particular adapter factory. In these cases, subclassing grokcore.component.Adapter or MultiAdapter is not possible. Instead, you can use the global_adapter() directive. Here is an example drawing on the ``z3c.form`` library, which provides an adapter factory factory for named widget attributes:: import zope.interface import zope.schema import grokcore.component import z3c.form.widget import ComputedWidgetAttribute class ISchema(Interface): """This schema will be used to power a z3c.form form""" field = zope.schema.TextLine(title=u"Sample field") ... label_override = z3c.form.widget.StaticWidgetAttribute( u"Override label", field=ISchema['field']) grokcore.component.global_adapter(label_override, name=u"label") In the example above, the provided and adapted interfaces are deduced from the object returned by the ``StaticWidgetAttribute`` factory. The full syntax for global_adapter is:: global_adapter(factory, (IAdapted1, IAdapted2,), IProvided, name=u"name") The factory must be a callable (the adapter factory). Adapted interfaces are given as a tuple. You may use a single interface instead of a one-element tuple for single adapters. The provided interface is given as shown. The name defaults to u"" (an unnamed adapter). Subscriber ---------- Here we see a subscriber much like it occurs within Zope itself. It subscribes to the modified event for all annotatable objects (in other words, objects that can have metadata associated with them). When invoked, it updates the Dublin Core 'Modified' property accordingly:: import datetime import grokcore.component from zope.annotation.interfaces import IAnnotatable from zope.lifecycleevent.interfaces import IObjectModifiedEvent from zope.dublincore.interfaces import IZopeDublinCore @grokcore.component.subscribe(IAnnotatable, IObjectModifiedEvent) def updateDublinCoreAfterModification(obj, event): """Updated the Dublin Core 'Modified' property when a modified event is sent for an object.""" IZopeDublinCore(obj).modified = datetime.datetime.utcnow() API overview ============ Base classes ------------ ``Adapter`` Base class for an adapter that adapts a single object (commonly referred to as the *context*). Use the ``context`` directive to specify which object to adapt and the ``implements`` directive to specify which interface the adapter will provide. If it's a named adapter, you may use the ``name`` directive to specify the name. ``MultiAdapter`` Base class for an adapter that adapts *n* objects (where *n>=1*). Use the ``adapts`` directive to specify which kinds of objects are adapted and the ``implements`` directive to specify which interface the adapter will provide. If it's a named multi-adapter, you may use the ``name`` directive to specify the name. ``GlobalUtility`` Base class for a globally registered utility. Unless you use the ``direct`` directive to indicate that the class itself should be registered as a utility, the class will automatically be instantiated, therefore the constructor may not take any arguments. Use the ``implements`` directive to specify which interface the utility provides, or if that is not unambiguous, also use the ``provides`` directive to specify which of the implemented interfaces should be used when registering the utility. If it's a named utility, you may use the ``name`` directive to specify the name. ``Context`` Subclasses of this will automatically be found as potential contexts for adapters and other types of context-dependent components. Class-level directives ---------------------- ``implements(iface1, iface2, ...)`` declares that a class implements the interfaces ``iface1``, ``iface2``, etc. It is identical to ``zope.interface.implements``. ``implementsOnly(iface1, iface2, ...)`` declares that a class *only* implements the interfaces ``iface1``, ``iface2``, etc. It is identical to ``zope.interface.implementsOnly``. ``classProvides(iface1, iface2, ...)`` declares that a class object (as opposed to instances of the class) provides the interfaces ``iface1``, ``iface2``, etc. It is identical to ``zope.interface.classProvides``. ``context(iface_or_class)`` declares the type of object that the adapter (or a similar context-dependent component) adapts. This can either be an interface (in this case all objects providing this interface will be eligible contexts for the adapter) or a class (then only instances of that particular class are eligible). ``adapts(iface_or_class1, iface_or_class_2, ...)`` declares the types of objects that a multi-adapter adapts. ``name(ascii_or_unicode)`` declares the name of a named utility, named adapter, etc. ``title(ascii_or_unicode)`` declares the human-readable title of a component (such as a permission, role, etc.) ``provides(iface)`` declares the interface that a utility provides (as opposed to potentially multiple interfaces that the class implements). ``direct()`` declares that a ``GlobalUtility`` class should be registered as a utility itself, rather than an instance of it. ``baseclass()`` declares that a subclass of an otherwise automatically configured component should not be registered, and that it serves as a base class instead. Module-level directives ----------------------- ``global_utility(class, [provides=iface, name=ascii_or_unicode, direct=bool])`` registers an instance of ``class`` (or ``class`` itself, depending on the value of the ``direct`` parameter) as a global utility. This allows you to register global utilities that don't inherit from the ``GlobalUtility`` base class. ``global_adapter(factory, [adapts=tuple_of_interfaces, provides=iface, name=ascii_or_unicode])`` registers the ``factory`` callable as a global adapter. The ``adapts`` argument may be a tuple of interfaces or a single interface, if this is a single adapter. Both ``adapts`` and ``provides`` will be deduced from information annotated onto the factory if necessary. If no adapted interface can be determined, the current context will be assumed. The name defaults to u"". This allows you to register global adapters that don't inherit from the ``Adapter`` or ``MultiAdapter`` base classes. Function decorators ------------------- ``@adapter(iface_or_class1, iface_or_class2, ..., name=u"name")`` registers the function as an adapter for the specific interface. The ``name`` argument must be a keyword argument and is optional. If given, a named adapter is registered. ``@implementer(iface1, iface2, ...)``` declares that the function implements a certain interface (or a number of interfaces). This is useful when a function serves as an object factory, e.g. as an adapter. ``@provider(iface1, iface2, ...)``` declares that the function object provides a certain interface (or a number of interfaces). This is akin to calling directlyProvides() on the function object. ``@subscribe(iface_or_class1, iface_or_class2, ...)`` declares that a function is to be registered as an event handler for the specified objects. Normally, an event handler is simply registered as a subscriber for the event interface. In case of object events, the event handler is registered as a subscriber for the object type and the event interface. Changes ======= 2.0 (2009-09-16) ---------------- * Use a newer version of Martian that has better support for inheritance. This is demonstrated in ``tests/inherit``. * The ``ContextGrokker`` and the ``scan.py`` module have gone away thanks the newer Martian. * Directive implementations (in their factory method) should *not* bind directives. Directive binding cannot take place at import time, but only at grok time. Binding directives during import time (when directives are executed) can lead to change problems. (we noticed this during our refactoring to use the new Martian). * Use 1.0b1 versions.cfg in Grok's release info instead of a local copy; a local copy for all grokcore packages is just too hard to maintain. 1.7 (2009-06-01) ---------------- * Add missing provider, global_adapter, implementsOnly, classProvides() to the module interface so that they are included in __all__ 1.6 (2009-04-10) ---------------- * Add convenience imports for implementsOnly() and classProvides() class declarations form zope.interface. * Add support for registering global adapters at module level:: grok.global_adapter(factory, (IAdapted1, IAdapted2,), IProvided, name=u"name") Only 'factory' is required. If only a single interface is adapted, the second argument may be a single interface instead of a tuple. If the component has declared adapted/provided interfaces, the second and third arguments may be omitted. * Add support for an @provider decorator to let a function directly provide an interface:: @grok.provider(IFoo, IBar) def some_function(): ... This is equivalent to doing alsoProvides(some_function, IFoo, IBar). * Add support for named adapters with the @adapter decorator:: @grok.adapter(IAdaptedOne, IAdaptedTwo, name=u"foo") def some_function(one, two): ... 1.5.1 (2008-07-28) ------------------ * The ``IGrokcoreComponentAPI`` interface was missing declarations for the ``title`` and ``description`` directives. 1.5 (2008-07-22) ---------------- * Fix https://bugs.launchpad.net/grok/+bug/242353: grokcore.component contains old-style test setup. There is no `register_all_tests` method in grokcore.component.testing anymore. Use z3c.testsetup instead. * Allow functions that have been marked with @grok.subscribe also be registered with ``zope.component.provideHandler()`` manually. This is useful for unit tests where you may not want to grok a whole module. * Document grokcore.component's public API in an interface, ``IGrokcoreComponentAPI``. When you now do:: from grokcore.component import * only the items documented in that interface will be imported into your local namespace. 1.4 (2008-06-11) ---------------- * Ported class grokkers to make use of further improvements in Martian. This requires Martian 0.10. 1.3 (2008-05-14) ---------------- * Ported class grokkers to make use of the new declarative way of retrieving directive information from a class. This requires Martian 0.9.6. 1.2.1 (2008-05-04) ------------------ * Upgrade to Martian 0.9.5, which has a slight change in the signature of ``scan_for_classes``. * Remove an unnecessary import ``methods_from_class`` from ``grokcore.component.scan``. 1.2 (2008-05-04) ---------------- * Ported directives to Martian's new directive implementation. As a result, nearly all helper functions that were available from ``grokcore.component.util`` have been removed. The functionality is mostly available from the directives themselves now. * The ``baseclass`` directive has been moved to Martian. * The ``order`` directive and its helper functions have been moved back to Grok, as it was of no general use, but very specific to viewlets. 1.1 (2008-05-03) ---------------- * ``determine_module_component`` now looks for classes that implement a certain interface (such as ``IContext``), instead of taking a list of classes. If looking for ``IContext``, it still will find ``Context`` subclasses, as these were also made to implement ``IContext``. * Move the ``public_methods_from_class`` helper function back to Grok, it isn't used at all in ``grokcore.component``. 1.0.1 (2008-05-02) ------------------ * The grokkers for adapters and global utilities did not use the correct value for the *provided* interface in the configuration action discriminator. Because of this, uninformative and potentially wrong conflict errors would occur, as well as no conflict where a conflict should have occurred. * The grokker for the ``global_utility()`` directive did immediate registrations instead of generating configuration actions. Therefore it did not provoke ``ConflictErrors`` for conflicting registrations. * Improved documentation 1.0 (2008-05-01) ---------------- * Created ``grokcore.component`` in March 2008 by factoring basic component base classes and their directives and grokkers out of Grok. http://pypi.python.org/pypi/grokcore.component Grok Team 22cd1dfb64e763412d361a860350d80bd6e7b039 2.0